1. Field of the Invention
The present invention relates to a grating to be used as a floor face in a tunnel, a corrosion resistant floor face, a floor board in a sewage treatment plant, walking passaage and the like.
2. Prior Art
Gratings have been conventionally manufactured of steel, but recently in cooperation with the development of glass fiber reinforced plastic (hereinafter referred to as "FRP") whose light weight and corrosion resistance properties are very advantageous in view of practical use, gratings of FRP are now widely used.
It is well known that gratings mainly composed of FRP are solidly formed by press working, otherwise are formed by assembling FRP components prepared by pultrusion with auxiliary members in such a manner as to have a specified distance between one component and the other.
FIG. 5 shows a grille grating which is solidly formed by press working with a metal pattern.
FIG. 6 shows an example of the aforementioned assembled grating, in which I-shaped drawn components 1a are one by one fitted laterally into insertion grooves provided in a spacer 5 to be laid in parallel, thus being assembled into a grid in appearance.
In the aforementioned conventional FRP gratings of the above construction, there exist several problems to be solved as follows:
(1) In the grating solidly formed by press working, the size of the grating is restricted, and it is impossible to manufacture a grating exceeding certain dimensions. Moreover, considering the property of the material, sufficient strength is not achieved when exceeding a certain size, and the grating manufactured by such a method is not recommended to put it in practical use.
(2) On the other hand, the components themselves prepared by drawing have a strength to a certain extent, but the formation of the grating by assembly is not economical because of the heavy weight of the components arranged with certain distances. Moreover, from the viewpoint of an assembled structure, the function of transmitting a load directly from one component to an adjacent one is insufficient, resulting in a concentration load limit at a rather low level.